Extracellular nucleotides (ATP, ADP and UTP) are known to activate type-2 purinergic (P2Y and P2X) receptors on platelets, endothelium and immune cells to induce vascular inflammation and thrombosis. Cellular ectonucleotidases hydrolyze P2-mediators to down regulate P2 receptor-signaling responses. CD39 is the dominant vascular, T regulatory and Natural Killer (NK)T cell ectonucleotidase/NTPDase and plays a crucial role in the ectonucleotidase cascade, involving CD73, to generate adenosine. This nucleoside has important antithrombotic and anti-inflammatory properties. The roles of CD39L1 (a preferential ecto-ATPase), expressed by adventitial cells, and CD39L3 (functionally akin to CD39) expressed by vascular endothelium, on thrombus formation are completely unexplored in vivo. Specific Aim 1: Study functional impacts of the three vascular CD39/NTPDases on thrombus formation in vivo. a) Evaluate and compare accumulation of CD39, CD39L1 and CD39L3 in generated thrombi, with platelet sequestration, associated tissue factor and fibrin deposition. b) Contrast the impact of vascular Cd39L1 and/or Cd39L3 deletion vs. global absence of Cd39 on arteriolar thrombus formation and platelet activation in mutant mice. Specific Aim 2: Thromboregulatory functions of immune cells in vivo a) Perform adoptive transfer of T regulatory cells expressing Cd39 to determine the role of immune regulatory cells on platelet activation and thrombus formation in vivo. b) Test mice following adoptive transfer of isolated NKT cells expressing Cd39 and Cd73 to determine impact on thrombus formation in vivo. Specific Aim 3: Association of CD39 with membrane proteins and lipids. Palmitoylation at the N-terminus targets CD39 to lipid rafts within cell membranes that are linked to microparticle formation. The C-terminus of CD39 binds apo-lipoprotein A2 and incorporates CD39 into High Density Lipoproteins (HDL). a) Explore structural and functional interactions of CD39 within lipid rafts. b) Examine how palmitoylation and other post-translational modifications of CD39 impact association with cholesterol and sphingomyelin. c) Determine effects of activation of acid sphingomyelinase and ceramide generation on CD39 bioactivity in endothelial cells, lymphocytes and their derived microparticles. d) Study thrombus formation in hyperlipidemic Cd39 mutant mice. This work will provide insights into the central thromboregulatory mechanisms impacting platelet activation and vascular injury in vivo.